In nature, many anadromous fish live most of their adulthood in seawater, but swim upstream to freshwater for the purpose of breeding. As a result, anadromous fish hatch from their eggs and are born in freshwater. As these fish grow, they swim downstream and gradually adapt to the seawater.
Fish hatcheries have experienced difficulty in raising these types of fish because the window of time in which the pre-adult fish adapts to seawater (e.g., undergoes smoltification) is short-lived, and can be difficult to pinpoint. As a result, these hatcheries experience significant morbidity and mortality when transferring anadromous fish from freshwater to seawater. Additionally, many of the fish that do survive the transfer from freshwater to seawater are stressed, and consequently, experience decreased feeding, and increased susceptibility to disease. Therefore, these anadromous fish often do not grow well after they are transferred to seawater.
The aquaculture industry loses millions of dollars each year due to problems it encounters in transferring pre-adult anadromous fish from freshwater to seawater. Hence, a need exists to improve methods involved in transferring pre-adult anadromous fish to seawater. A further need exists to increase survival, and reduce stress, of pre-adult anadromous fish that have been transferred to seawater.
The present invention relates to methods for improving the raising of pre-adult anadromous fish or preparing these fish for transfer to seawater by increasing expression of a receptor, referred to as the Polyvalent Cation Sensing Receptor (PVCR). The expression and/or sensitivity of the PVCR is increased by subjecting the pre-adult anadromous fish to calcium and magnesium. The pre-adult anadromous fish are subjected to the calcium and magnesium when they are added to the freshwater environment. The invention encompasses adding calcium and magnesium to the freshwater, and adding feed for fish consumption to the freshwater. The feed contains sodium chloride (NaCl) in an amount to contribute to a significantly increased level of calcium and/or magnesium in the serum of the pre-adult anadromous fish. Increased expression and/or sensitivity of the PVCR is maintained until the fish are ready to be transferred to seawater. The pre-adult anadromous fish can be maintained in the freshwater having calcium and magnesium until they are ready to be transferred to seawater.
In one embodiment of the invention, pre-adult anadromous fish (e.g., salmon, trout and arctic char) are prepared for transfer from freshwater to seawater by adding calcium and magnesium to the freshwater, and adding feed for fish consumption having between about 1% and about 10% NaCl by weight (e.g. between about 10,000 mg/kg and 100,000 mg/kg) to the freshwater. The amount of calcium added to the freshwater is an amount sufficient to bring the concentration up to between about 2.0 mM and about 10.0 mM, and the amount of magnesium added is an amount sufficient to bring the concentration up to between about 0.5 mM and about 10.0 mM. The present invention also includes, optionally, exposing the pre-adult anadromous fish to a photoperiod. Preferably, the photoperiod is continuous (e.g., for a continuous period of between about 12 hours and about 24 hours in a 24 hour period).
Additional embodiments of the invention include methods of increasing or improving food consumption before and/or after seawater transfer, increasing survival and/or reducing mortality, reducing osmotic damage, transferring parr (e.g., between about 10 and about 60 grams) to seawater, and transferring a pre-adult anadromous fish to seawater having a temperature of about 14xc2x0 C. to about 19xc2x0 C. These methods are performed by adding calcium and magnesium to the freshwater, subjecting or exposing the pre-adult anadromous fish to calcium and magnesium, or introducing the pre-adult anadromous fish to freshwater having calcium and magnesium, in amounts sufficient to increase expression and/or sensitivity of the PVCR. The methods also involve adding feed having between about 1% and about 10% NaCl by weight to the freshwater and transferring the pre-adult anadromous fish to seawater.
In other embodiments, the invention encompasses detection assays for diagnostic purposes or methods of determining whether a pre-adult anadromous fish, that are subjected to calcium and magnesium in the freshwater, and are fed with feed having between about 1% and about 10% NaCl by weight, are ready for transfer to seawater, by assessing the amount of PVCR expression in the pre-adult anadromous fish. An increased level of expression and/or sensitivity, as compared to a control (e.g., PVCR expression from a fish not subjected to calcium and magnesium), indicates that the pre-adult anadromous fish are ready for transfer to seawater. In a preferred embodiment, the assay includes contacting an anti-PVCR antibody with a sample (e.g., gill, skin, intestine, urinary bladder, kidney, brain or muscle) under conditions sufficient for the formation of a complex between the antibody and the PVCR; and detecting the formation of the complex. In another embodiment the assay relates to hybridizing a nucleic acid sequence having a detectable label to the nucleic acid sequence of the PVCR of a sample taken from the pre-adult anadromous fish and detecting the hybridization.
In yet another embodiment, the present invention relates to various compositions and mixtures. In particular, the invention pertains to an aquatic food composition having a concentration of NaCl between about 10,000 mg/kg and 100,000 mg/kg (e.g., about 12,000 mg/kg).
The invention also embodies an aquatic mixture for providing an environment to improve the raising of pre-adult anadromous fish. The mixture includes calcium and magnesium. An example of such a mixture is a calcium source, that when added to freshwater, provides a concentration of between about 2.0 mM and about 10.0 mM; and a magnesium source, that when added to freshwater, provides a concentration of between about 0.5 mM and 10.0 mM.
In yet another embodiment, the present invention relates to kits. In particular, the invention embodies kits for improving the raising of pre-adult anadromous fish, that includes calcium and magnesium for addition to the freshwater and an aquatic food composition, as described herein. In another embodiment, the invention includes kits for determining whether a pre-adult anadromous fish are ready for transfer to seawater, after being subjected to calcium and magnesium in freshwater, and feed having between about 1% and about 10% NaCl by weight. The kit includes either an anti-PVCR antibody, and a solid support; or a nucleic acid sequence having a detectable label that can hybridize to nucleic acid of an aquatic PVCR.
Surprisingly, it has been discovered that increased expression and/or altering the sensitivity of the PVCR allows these pre-adult anadromous fish to better adapt to seawater. Until the discovery of the present invention, the aquaculture industry was unable to transfer the pre-adult anadromous fish to seawater without subjecting the fish to stress, death and/or disease. Unlike this practice, carrying out the steps of the invention increases the expression and/or alters the sensitivity of the PVCR and allows for transfer of the pre-adult anadromous fish to seawater with minimal or no stress, death and/or disease, and unexpectedly provides several benefits, such as the ability to transfer these fish to water having higher temperatures, as further described herein. The present invention results in one or more of the following advantages in transferring pre-adult anadromous fish to seawater: a reduction in mortality; improvement in feeding; a decrease in the amount of diseased fish; and/or a reduction in osmotic shock. The present invention also allows for earlier harvesting of the fish with increased flexibility in producing fish year round. Additionally, the methods of the present invention can result in significant cost savings for fish hatcheries.